Integrated circuit manufacturers strive to have a wide variety of integrated circuit types to satisfy their customers' needs. Many of these different types are minor modifications of chips that are fundamentally similar. For example, 1-bit output data (.times.1), 4-bit output data (.times.4), 8-bit output data (.times.8), static column and page modes are available in dynamic random access memories (DRAMs). Each of these modes may help the performance of a system in its own particular way. However, fundamentally each provides the function of storing a set amount of data.
In order to expedite design time and minimize manufacturing costs, integrated circuit manufacturers have designed several mode types into a fundamental design. Some of these multiple design integrated circuits are programmed by providing different metal configurations in the last metallization step. The photomasking for this metallization step may be easily changed in the production line or partially finished integrated circuits may be stored in order to quickly perform the final masking step and quickly provide the desired integrated circuit to the customer. This has been an effective strategy in the industry, but still requires changes to be made in the relatively complicated metallization masking step of the integrated circuit fabrication process. Another draw back of this strategy is that the integrated circuit remains vulnerable to contamination until the final protective layers are over the top of the integrated circuit.
In another programming technique, bond pad programming, the programming step is moved downstream from the integrated circuit manufacturing process to the packaging step. The options desired are chosen by selectively bonding programming bond pads to Vdd or Vss. In some instances, some of the bonding pads may be left unbonded. If a pad is left unbonded, the pad is taken to a default potential on chip. The necessary reconfiguration within the chip for the desired mode of operation is accomplished through setting of logic gates and use of CMOS transfer devices. Selection at this stage of manufacturing puts the decision closer to the point of customer delivery and allows the marketing and manufacturing organizations greater flexibility in servicing the customer's needs.
The use of bond pad programming leads to an interesting possibility--letting the customer himself determine the option he wants at the point of use, his board. If a way can be found for him to do so, without increasing the cost of the device or his system costs, then there appear to be advantages for both the manufacturer and the user. Having a single device from which to source all device options solves his inventory problems for multiple device types while freeing his designers to choose the best device for the application. In both cases it simplifies the question of product mix from "how many of which kind?" to simply "how many?"